Before reading this, I want to remind you English is NOT my born language, I'm a frenchie who TRY to write something in english. Hope you can enjoy that short fanfic with all the grammatical mistakes.
-KACCHAN TAKE ERI WITH YOU AND RUN!
U.A. Is on fire, the school is almost destroyed, the grass is covered with bodies, most of thems are dead or badly injuried, a army of villains walking on the destroyed gate, Gigantomachina smashing everything that crossed his path advancing toward the school, the war is over and the heroes have lost.
All For One have escaped Tartarus few days ago, relasing every villains with him and destroying the prison behind him, since when, he have call every villains toward him and get a army under his command. He launch his attack the day of the sport festival, knowing the principal of U.A. will not delay the event, it was a mistake from the heroes side. Even if security was upgraded, and almost every heros from the top 10 where present and even more it was a real massacre. Not even 2 hours after the beginning of the invasion the fight was over, and HE have won. All For One is now marching on U.A. ground, 2 goonies behind him carrying 2 bodies and throw thems on the ground, it was the bodies of the former number one hero All Might and the present number one Endeavor, both of thems obviously dead. All For One attrack at him a mic with a TK quirk he have stole in his live and check if it still work.
-People of Japan, I present myself, I am All For One, the true ruler of Japan from now. As you can see your precious heroes have lost and I declare myself the true ruler of Japan. No one can stand in my way, for centuries I stay in the shadow ruling the underworld but now I decided I step up in the light and annonce my awakening. No one can match my power, not even your precious top 10 ranking heroes. Look at thems, look at your precious All Might, lying at my feets like the insect he is. There is only one hero I challenge to facing me now, you hear me Deku? Come and fight me 9th holder of my late brother quirk, come and face me once and for all. We will end this parody of endless battles bewteen All For One and One For All. Come at me Deku, i'm waiting for you, every one of my soldier have been instructed to not fighting you and only lead you to me, so the world can witness the end of the heroes age, don't make me wait!
During this time Izuku, Katsuki and Eri where hiding in one of U.A. training ground, a inconcious Eri in bakugo's arm, himself having a few bruises on his face and body but not really injuried and next to him a badly injuried Deku. His right arm have been decaying from his body by Shigaraki and he have a nasty cut on his chest.
-Kacchan, Take Eri with you and escape this place, I will hold him long enough for you to escape by the underground hideway Aizawa sensei have show us one day.
-Fuck you Deku, I will not flea a battle.
-You need to.
-DON'T TELL ME WHAT TO DO DEKU!
-LISTEN TO ME FOR ONCE IN YOUR FREAKING LIFE KACCHAN, IT'S OVER OKAY, WE LOOSE. WE HAVE FUCKING LOOSE THE WAR AND SHE IS OUR LAST HOPE.
-What do you mean Deku?
-I'm dying Kacchan, I have lost too much blood and i'm down at one arm, I can't fight him anymore and win but I can stall him long enough for you to escape and get to safety.
-No fucking way Deku.
-You know it's the only thing to do.
He open Eri's mouth and let a few drops of blood enter her mouth and watch her swallow it while being unconcious. He know she got One For All, he feel the quirk have been passed to her.
-I have give her One For All, now it's up to you to protect her! Please Kacchan, hide her and train her, she is all we have left. She is 15 now, old enough to use the quirk without risquing her life and her rewind quirk will help her heal her body to mastered it. I will go fight him here and you will have all the time to escape and I know you will do everything you can to help her. There is a private plane at the end of the tunnel, use it and fly to china, from here go the the USA, you will be able to hide in that country.
-And you Deku? You planing to fight him and die in a pathetic way?
-Not in a pathetic way. Before dying Momo gave me something, it's a mini nuclear bomb. I'll grab him, Shigaraki and Gigantomachina with black whip and I'll fly us the higher I can before detonate it. He will probably survive it but he will be very hurt, leaving you alone for a few years, giving you enough time to train her to finish it. Can I count on you Kacchan?
-Thisk! I...I'll do it Deku, you fucking nerd, i'll take care of little unicorn and se will finish the job.
-Thanks Kacchan and...I will miss you, my friend!
-Yeah, I will miss you too Deku. Now go and make thems pay for what they do to Ochako!
-Don't worry, they will pay.
-Hey Deku!
-Yes Kacchan?
-Good luck, Izuku!
-You too, Katsuki!
Bakugo run with Eri in his arm without looking back, he know if he watch Deku one more time he will turn around and goes fighting the fucker with him but he make him a promess, and he will be damned if he broke it. He found the hiddend tunnel and run as long as his legs let him go. After a run who feel like a eternety to him the ground start shaking and a extremly loud boum have been hear. He know Deku have accomplish his mission, and now it's time to for him to begin his. He found the plane in the hidden garage and climb it, placing the unconcious girl next to him.
A few days later the entire world is mourning every heros who die in japan during what is now called the dark day. Footage show the wounded hero Deku grabbing the called All For One and 2 other villains with what is look like a dark energy binding quirk before taking off in the air and flying in the atmosphere before a powerfull explosion can be seen froms kilometers. Experts determined the explosion was a nuclear one but the radiation where almost all scattered in the higher layer of the atmosphere. The entire world was cheering at the hero's sacrifice, with his action defeating the most vicious and violent villain of Japan's history.
No one know All For One barely survive the explosion and have been taking away by his most precious subordinate the mist nomu Kurogiri. His body is almost destroyed but a quirk he stole a few decade back maintain him alive, but he is now in a very bad shape, without arms or legs, plugged on a articifial breathing system and maintained alive by intravenous infusion, obliged to be feeded of painkiller non-stop due to the extreme pain he suffer every second of his existence. Kurogiri kidnapp somes of the world best doctors to taking care of his master, forcing thems to either heal him or making him a new body.
It will take thems almost a decade to gather the technology needed to put him back on his feets, with a body almost entirely made of machine part, letting him controling this cybernetic body by stealing a technology controling quirk. Soon All for One make his grand return to Japan, attaking the newly rebuilded U.A. School with a small army he gather during his incapacited years but this time the heroes where ready, leaded by the Veterant hero Nitro, also know as Katsuki Bakugo and his protegee, the hopefull heroine Eri, this time they have swear the villains will not win, not today, not any other days ever.
No one know what really happened that day, witnesses of the fight claim the young heroine Eri have a fistfull fight with the now Cyborg All For One before the horn on her head start to grow and glow a pink color, a few minutes later nothing was left of the body of the villain, only the heroine claiming he was definitly gone without any chanse to come back, with a smile on her face and tears on her eyes.